Retransmission schemes based on LLR combining in WLAN

ABSTRACT

Embodiments of the present invention provide a method and apparatus for enhanced data retransmission based on log-likelihood ratio (LLR) combining in WLAN. According to some embodiments, packets can be retransmitted using a modified transmission scheme. Packets that are received with an error are stored, and a subsequent packet is received that includes data that can be used to correct the error. For example, each packet can be encoded for both error detection and correction, and the retransmission mechanism can be adapted to the error rate. The retransmission scheme is improved by utilizing an LLR combining scheme, transmit diversity, and modified ACK methods.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of and priority to provisionalpatent application Ser. No. 62/743,010, with a filing date of Oct. 9,2018, which is hereby incorporated by reference in its entirety.

FIELD

Embodiments of the present invention generally relate to the field ofwireless communications. More specifically, embodiments of the presentinvention relate to systems and methods for efficiently managingretransmission of data in a wireless network.

BACKGROUND

Modern electronic devices typically send and receive data with otherelectronic devices wirelessly using Wi-Fi, and often data that is sentby a transmitter to a receiver is lost or corrupted. This can be due tointerference from other electronic device, or other common issues withwireless transmission of data, such as weather or obstructions thatphysically block the wireless signal. For these reasons, severaltechniques for retransmitting data have been developed so that dataintended for the receiver can be delivered successfully, even ifretransmission is required.

Two common techniques for retransmitting data are Automatic RepeatRequest (ARQ) and Forward Error Coding (FEC). ARQ is a technique thatrequires the receiver to send an acknowledgement (“ACK”) packet whendata has been received successfully. If the data is not deliveredsuccessfully or delivered with an error, no ACK is sent to thetransmitter. In this case, when the transmitter does not receive an ACK,the data is retransmitted. While this approach leads to very highreliability when transmitting data, sending an ACK for every data packetthat is successfully received leads to decreased throughput when errorsoccur frequently in the channel.

FEC is a technique that allows a receiver to correct errors in thetransmission using error coding and metadata. For instance, data can besent with a cyclic redundancy check (CRC) digest. FEC reduces errors andonly moderately decreases throughput. However, the use of FEC does notlead to high reliability, as some errors may not be able to be correctedusing the error coding.

Hybrid automatic repeat request (hybrid ARQ or HARQ) combines high-rateforward error-correcting coding and ARQ error-control. In standard ARQ,redundant bits are added to data to be transmitted based on anerror-detecting (ED) code such as a CRC as referred to above. Receiversdetecting a corrupted message request a new message from the sender, theoriginal data is encoded with a forward error correction (FEC) code, andthe parity bits are sent along with the message or transmitted uponrequest when a receiver detects an error. Hybrid ARQ performs betterthan ordinary ARQ in poor signal conditions, but in its simplest formthis comes at the expense of significantly lower throughput in goodsignal conditions.

What is needed is an approach to data retransmission that provides highreliability without significantly reducing the throughput fortransmitting data between a transmitter and a receiver in a wirelessnetwork.

SUMMARY

Accordingly, embodiments of the present invention provide a method andapparatus for enhanced data retransmission in a wireless network basedon log-likelihood ratio (LLR) combining in WLAN. According to someembodiments, packets can be retransmitted using a modified transmissionscheme. Packets that are received with an error are stored, and asubsequent packet is received that includes data that can be used incombination with the stored data to correct the error. For example, eachpacket can be encoded for both error detection and correction, and theretransmission mechanism can be adapted to the error rate. Theretransmission scheme is improved by utilizing an LLR combining scheme,transmit diversity, and modified ACK methods.

According to one embodiment, a method of data retransmission in awireless network. The method includes transmitting a wireless packetincluding an aggregated MAC Protocol Data Unit (AMPDU) including aplurality of MAC Protocol Data Units (MPDUs) and codewords associatedwith the MPDUs, receiving an acknowledgement from a receiver indicatingfailed MPDUs of the AMPDU that were received with error, where thereceiver stores log-likelihood ratios (LLRs) for a set of codewordsassociated with the failed MPDUs, and responsive to the acknowledgement,retransmitting the retransmitted set of codewords to the receiver, wherethe receiver combines the set of codewords with the codewords associatedwith the MPDUs using the stored LLRs to generate combined codewords,where the receiver decodes the combined codewords to generate decodedcodewords, and where the receiver resolves the MPDUs of the AMPDU usingthe decoded codewords.

According to some embodiments, the codewords associated with the MPDUsand the retransmitted set of codewords include LDCP codewords, and wherethe wireless network is a WiFi network.

According to some embodiments, the transmitting a wireless packetincluding an AMPDU includes using a first transmit diversity scheme, andwhere the retransmitting the set of codewords includes using the firsttransmit diversity scheme.

According to some embodiments, the transmitting a wireless packetincluding an AMPDU includes using a first transmit diversity scheme, andwhere the retransmitting the set of codewords includes using a secondtransmit diversity scheme.

According to some embodiments, retransmitting the set of codewordsincludes retransmitting a minimum set of codewords that contain thefailed MPDUs.

According to some embodiments, the acknowledgement is a blockacknowledgment (BA), and the method includes identifying the minimum setof codewords required to be retransmitted based on an index of the BA.

According to some embodiments, the MPDUs are segmented and where eachcodeword is associated with a respective single MPDU.

According to a different embodiment, a method of data retransmission ina wireless network is disclosed. The method includes receiving awireless aggregated MAC Protocol Data Unit (AMPDU) including a pluralityof MAC Protocol Data Units (MPDUs) and codewords associated with theMPDUs from a transmitter of the wireless network, transmitting awireless acknowledgement to the transmitter indicating failed MPDUs ofthe AMPDU that were received with error, storing log-likelihood ratios(LLRs) in memory for a set of codewords associated with the failedMPDUs, receiving a wirelessly retransmitted set of codewords over thewireless network, combining the retransmitted set of codewords with thecodewords associated with the MPDUs using the stored LLRs to generatecombined codewords, decoding the combined codewords to generate decodeddata, and resolving the MPDUs of the AMPDU using the decoded data.

According to another embodiment, a system for data retransmission in awireless network is disclosed. The system includes a wirelesstransmitter and a wireless receiver. The transmitter is operable totransmit an aggregated MAC Protocol Data Unit (AMPDU) including aplurality of MAC Protocol Data Units (MPDUs) and codewords associatedwith the MPDUs to the receiver, the receiver is operable to transmit acodeword acknowledgement (CA) to the transmitter, where the CA indicatesfailed codewords of the AMPDU that were received with error to thetransmitter, the receiver is operable to store log-likelihood ratios(LLRs) in memory for the failed codewords, the transmitter is operableto retransmit the failed codewords to the receiver, the receiver isoperable to combine the retransmitted failed codewords with the failedcodewords associated with the AMPDU using the stored LLRs to generatecombined codewords, the receiver is operable to decode the combinedcodewords to generate decoded data, and the receiver is operable toresolve the MPDUs of the AMPDU using the decoded data.

According to some embodiments, the codewords and the retransmittedfailed codewords include LDCP codewords, and where the wireless networkis a WiFi wireless network.

According to some embodiments, the AMPDU is transmitted by thetransmitter using a first transmit diversity scheme, and where thefailed codewords are retransmitted by the transmitter using the firsttransmit diversity scheme.

According to some embodiments, the first transmit diversity schemeincludes at least one of: frequency diversity, and spatial diversity.

According to some embodiments, where the AMPDU is transmitted by thetransmitter using a first transmit diversity scheme, where the failedcodewords are retransmitted by the transmitter using a second transmitdiversity scheme, and where the first and second transmit diversityschemes are different.

According to some embodiments, the first transmit diversity scheme andthe second transmit diversity scheme include transmitting data using atleast one of: different frequency segments, different tone interweavers,different spatial streams, different beamforming techniques, anddifferent quadrature amplitude modulation.

According to some embodiments, the transmitter is operable to retransmitthe failed codewords to the receiver using an enacted retransmissionpacket including a PHY header, and where the PHY header includes a SIGfield indicating a modulation scheme used to retransmit the failedcodewords.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthis specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention:

FIG. 1 is a block diagram showing wireless data packets transmitted inan exemplary re-transmission scheme for communications between atransmitter and a receiver in a wireless network depicted according toembodiments of the present invention.

FIG. 2 is a block diagram showing segmented wireless data packetstransmitted in an exemplary re-transmission scheme for communicationsbetween a transmitter and a receiver depicted according to embodimentsof the present invention.

FIG. 3A is a block diagram showing wireless data packets transmitted inan exemplary re-transmission scheme using codeword acknowledgement (CA)for communications between a transmitter and a receiver depictedaccording to embodiments of the present invention.

FIG. 3B is a flowchart of an exemplary re-transmission scheme for awireless network depicted according to embodiments of the presentinvention.

FIG. 4 is a block diagram of operations and procedures for implementingan enhanced retransmission scheme for a wireless network depictedaccording to embodiments of the present invention.

FIG. 5 is a block diagram of operations and procedures for implementingan enhanced retransmission scheme using a wireless data packet having aPHY header or MAC header that includes a HARQ Enable field depictedaccording to embodiments of the present invention.

FIG. 6 is a block diagram of an exemplary format of an enhancedretransmission packet for a wireless network depicted according toembodiments of the present invention.

FIG. 7 is a block diagram of an exemplary format of an enhancedretransmission packet for a wireless network, the packet including a MACheader depicted according to embodiments of the present invention.

FIG. 8A is a block diagram of an exemplary format of an enhancedretransmission packet including codewords appended to a PSDU depictedaccording to embodiments of the present invention for a wirelessnetwork.

FIG. 8B is a block diagram of an exemplary format of an enhancedretransmission packet including codewords prepended to a PSDU depictedaccording to embodiments of the present invention for a wirelessnetwork.

FIG. 9A is a block diagram of an exemplary PPDU including a HARQ SIGfield depicted according to embodiments of the present invention.

FIG. 9B is a block diagram of an exemplary MU PPDU including a HARQ SIGfield depicted according to embodiments of the present invention.

FIG. 10 is a block diagram of an exemplary computer system upon whichembodiments of the present invention may be implemented.

DETAILED DESCRIPTION

Reference will now be made in detail to several embodiments. While thesubject matter will be described in conjunction with the alternativeembodiments, it will be understood that they are not intended to limitthe claimed subject matter to these embodiments. On the contrary, theclaimed subject matter is intended to cover alternative, modifications,and equivalents, which may be included within the spirit and scope ofthe claimed subject matter as defined by the appended claims.

Furthermore, in the following detailed description, numerous specificdetails are set forth in order to provide a thorough understanding ofthe claimed subject matter. However, it will be recognized by oneskilled in the art that embodiments may be practiced without thesespecific details or with equivalents thereof. In other instances,well-known methods, procedures, components, and circuits have not beendescribed in detail as not to unnecessarily obscure aspects and featuresof the subject matter.

Portions of the detailed description that follow are presented anddiscussed in terms of a method. Although steps and sequencing thereofare disclosed in a figure herein (e.g., FIG. 3B) describing theoperations of this method, such steps and sequencing are exemplary.Embodiments are well suited to performing various other steps orvariations of the steps recited in the flowchart of the figure herein,and in a sequence other than that depicted and described herein.

Some portions of the detailed description are presented in terms ofprocedures, steps, logic blocks, processing, and other symbolicrepresentations of operations on data bits that can be performed oncomputer memory. These descriptions and representations are the meansused by those skilled in the data processing arts to most effectivelyconvey the substance of their work to others skilled in the art. Aprocedure, computer-executed step, logic block, process, etc., is here,and generally, conceived to be a self-consistent sequence of steps orinstructions leading to a desired result. The steps are those requiringphysical manipulations of physical quantities. Usually, though notnecessarily, these quantities take the form of electrical or magneticsignals capable of being stored, transferred, combined, compared, andotherwise manipulated in a computer system. It has proven convenient attimes, principally for reasons of common usage, to refer to thesesignals as bits, values, elements, symbols, characters, terms, numbers,or the like.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise as apparent from the followingdiscussions, it is appreciated that throughout, discussions utilizingterms such as “accessing,” “writing,” “including,” “storing,”“transmitting,” “associating,” “identifying,” “encoding,” or the like,refer to the action and processes of a computer system, or similarelectronic computing device, that manipulates and transforms datarepresented as physical (electronic) quantities within the computersystem's registers and memories into other data similarly represented asphysical quantities within the computer system memories or registers orother such information storage, transmission or display devices.

Retransmission Schemes Based on LLR Combining in WLAN

Embodiments of the present invention provide a method and apparatus forenhanced data retransmission based on log-likelihood ratio (LLR)combining in WLAN. According to some embodiments, wireless data packetscan be retransmitted to a receiver station using a modified transmissionscheme. Packets that are received with an error are stored by thereceiver, and a subsequent packet is retransmitted and received thatincludes data that can be used to correct the error. For example, eachpacket can be encoded for both error detection and correction, and theretransmission mechanism can be adapted to the error rate. Theretransmission scheme is improved by utilizing an LLR combining scheme,transmit diversity, and modified ACK methods. These are furtherdescribed below.

LLR combining is also known as Chase Combining and involves a receivercombining multiple received copies of a coded packet. Transmit diversityis applied on re-transmission in certain embodiments to improve signalreception. According to some embodiments of the present invention, atransmitter transmits an aggregated MAC protocol data unit (AMPDU), andthe receiver responds with a block acknowledgement (BA) indicating whichMac protocol data units (MPDUs) of the AMPDU have not been receivedsuccessfully. A BA is a packet that includes multiple acknowledgements,for example, represented by a bitmap indicating which packets orportions have been received successfully.

The transmitter retransmits the missed MPDUs using various transmitdiversity schemes. The transmit diversity schemes can include frequencydiversity, spatial diversity, or a combination of both. In one exampleof transmit diversity, the retransmitted symbols can be mapped ondifferent frequency segments to use different tone interleavers. Inanother example of transmit diversity, the retransmit symbols can bemapped on different spatial streams, e.g., a different antennae, orusing different beam forming techniques. The transmit diversity schemecan also include different modulation mapping to introduce extra codinggain. For example, a different quadrature amplitude modulation (QAM)mapping can be used to change the reliability of different coded bits.By retransmitting packets using transmit diversity, the chances that theretransmitted packet is received successfully are increased. One or moreof the transmit diversity schemes described above can be used onsubsequent retransmissions.

With regard to FIG. 1, a block diagram 100 showing wireless packetstransmitted in an exemplary re-transmission scheme for communicationsbetween a transmitter and a receiver is depicted according toembodiments of the present invention. PHY Preamble 115 includesinformation indicating how to decode LDPC codewords included in thetransmission. The LDCP codewords (CW) are not aligned with the MPDUs inthis example, and therefore some codewords, e.g., CW #3 130, may beassociated with two MPDUs. The transmission may include any N number ofMPDUs contained in AMPDU 145, and any M number of codewords associatedwith the MPDUs. The payload of the retransmitted packets include thesame encoded bits as the missed codewords from the previoustransmission. The codewords can be decoded by the receiver and combinedwith codewords of retransmitted packets using stored LLR values from theoriginal transmission to resolve the missing MPDUs.

MPDU #1 105 is associated with codewords CW #1 120, CW #2 125, and CW #3130. MPDU #2 110 is associated with codewords CW #3 130, CW #4 135, andCW #5 140. In the example of FIG. 1, MPDU #1 105 is assumed to bereceived successfully by the receiver in the original transmission, andMPDU #2 110 is not received successfully. In this case, the receiverstores the LLRs for codewords CW #3 130, CW #4 135, and CW #5 140associated with MPDU #2 110. The receiver stores the received data andsends a BA to the transmitter. The BA includes an MPDU index andindicates that MPDU #1 105 was received successfully and that MPDU #2110 was not received successfully. For example, the BA can include abitmap representing an acknowledgment bit for each of the MPDUstransmitted successfully (or not) in the original transmission.

After receiving the BA, the transmitter identifies codewords CW #3 130,CW #4 135, and CW #5 140 associated with MPDU #2 110 from the MPDU indexin the BA. The transmitter then responsive to the BA retransmits theminimum set of codewords CW #3 130, CW #4 135, and CW #5 140. Accordingto some embodiments, the transmitter retransmits the minimum set ofcodewords CW #3 130, CW #4 135, and CW #5 140 using a different transmitdiversity scheme from the original transmission. The receiver thencombines the retransmitted codewords CW #3 130, CW #4 135, and CW #5 140with the codewords from the original transmission using the stored LLRvalues to decode the codewords. The MPDU #2 110 is resolved from thedecoded data.

With regard to FIG. 2, a block diagram 200 showing wireless packetstransmitted in an exemplary re-transmission scheme for communicationsbetween a transmitter and a receiver using BAs and segmentation isdepicted according to embodiments of the present invention. PHY Preamble215 includes information indicating how to decode LDPC codewordsincluded in the transmission. In this example, the LDCP codewords aresegmented to align with the MPDUs, and therefore the codewords arealways associated with exactly one MPDU. The transmission may includeany N number of MPDUs contained in AMPDU 240, and any M number ofcodewords associated with the MPDUs. The payload of the retransmittedpackets include the same encoded bits as the missed codewords from theprevious transmission. The codewords can be decoded by the receiver,stored, and combined with codewords of retransmitted packets usingstored LLR values from the original transmission to resolve the missingMPDUs.

In one embodiment, the MPDUs can be aligned with the codewords by addingpadding to the codewords at the transmitter. For example, the MPDUs maybe delimited without having a fixed size, and the MAC header includesinformation regarding the delimiters. The transmitter adds limitedpadding to the codewords to generate aligned coding block for moreefficient retransmission.

MPDU #1 205 is associated with codewords CW #1 220, CW #2 225, and MPDU#2 210 is associated with codewords CW #3 230 and CW #4 235. In theexample of FIG. 2, MPDU #1 205 is assumed to be received successfully bythe receiver in the original transmission, and MPDU #2 210 is notreceived successfully. In this case, the receiver stores the LLRs forcodewords CW #3 230 and CW #4 235 associated with MPDU #2 210. Thereceiver sends a BA to the transmitter. The BA includes an MPDU indexand indicates that MPDU #1 205 was received successfully and that MPDU#2 210 was not received successfully. For example, the BA can include abitmap representing an acknowledgment bit of each of the MPDUstransmitted successfully (or not) in the original transmission.

After receiving the BA, the transmitter identifies codewords CW #3 230and CW #4 235 associated with MPDU #2 210 from the MPDU index in the BA.The transmitter retransmits the minimum set of codewords CW #3 230 andCW #4 235. According to some embodiments, the transmitter retransmitsthe minimum set of codewords CW #3 230 and CW #4 235 using a differenttransmit diversity scheme from the original transmission. The receiverthen combines the retransmitted codewords CW #3 230 and CW #4 235 withthe codewords stored from the original transmission using the stored LLRvalues to decode the codewords. The MPDU #2 210 is resolved from thedecoded data.

With regard to FIG. 3A, a block diagram 300 showing wireless packetstransmitted in an exemplary re-transmission scheme for communicationsbetween a transmitter and a receiver in a wireless network where thescheme uses codeword acknowledgment (CA) is depicted according toembodiments of the present invention. Using CAs to acknowledge receivedcodewords requires that each codeword contains its own cyclic redundancycheck (CRC) so that the receiver can detect if the codeword is receivedwithout error. The receiver can respond to the transmitter with CAs toindicate which specific codewords were not delivered successfully in theoriginal transmission. The CA may contain a respective bit for eachcodeword to indicate successful receipt or not of the codeword.

PHY Preamble 315 includes information indicating how to decode LDPCcodewords included in the transmission. The LDCP codewords are notaligned with the MPDUs in this example, and therefore some codewords,e.g., CW #3 330, may be associated with two MPDUs. The transmission mayinclude any N number of MPDUs contained in AMPDU 350, and any M numberof codewords associated with the MPDUs. The payloads of theretransmitted packets include the same encoded bits as the missedcodewords from the previous transmission. The codewords can be decodedby the receiver and combined with codewords of retransmitted packetsusing stored LLR values from the original transmission to resolve themissing MPDUs.

MPDU #1 305 is associated with codewords CW #1 320, CW #2 325, and CW #3330, and MPDU #2 310 is associated with codewords CW #3 330, CW #4 335,and CW #5 340. In the example of FIG. 3A, CW #2 325 and CW #5 340 areassumed to not be received successfully by the receiver in the originaltransmission. In this case, the receiver stores the LLRs for codewordsCW #2 325 and CW #5 340. The receiver sends a CA to the transmitterindicating that CW #2 325 and CW #5 340 were not delivered successfullyto the receiver. The transmitter in response to the CA then identifiesCW #2 325 and CW #5 340 from the CA and re-transmits CW #2 325 and CW #5340. According to some embodiments, the transmitter retransmits CW #2325 and CW #5 340 using a different transmit diversity scheme from theoriginal transmission. The receiver then combines the retransmittedcodewords CW #2 325 and CW #5 340 with the codewords from the originaltransmission using the stored LLR values to decode the codewords. TheMPDU #1 305 and MPDU #2 310 are resolved from the decoded data.

With regard to FIG. 3B, a flowchart of an exemplary wirelessre-transmission scheme 370 is depicted according to embodiments of thepresent invention. The re-transmission scheme 370 includes performingchase combining at the receiver by retransmitting a minimum set of LDPCcodewords.

At step 375, the transmitter transmits an AMPDU to the receiver station.

At step 380, the receiver responds with an ACK (e.g., a BA or CA)indicating which MPDUs or codewords have not been received successfully.The receiver also stores the LLR in memory for the minimum set of LDPCcodewords that contain the failed MPDUs. The minimum set of LDPCcodewords that contains an MPDU or a group of MPDUs are pre-determinedby the transmitter and the receiver and are stored at the receiver.

At step 385, the transmitter retransmits the minimum set of LDPCcodewords using a transmit diversity scheme. The re-transmission andtransmit diversity scheme is indicated in the retransmit packet. Thetransmitter can identify the minimum set of LDPC codewords that need tobe retransmitted based on the failed MPDU index included in the BA orCA. According to some embodiments, the transmitter retransmits theminimum set of LDPC codewords using a different transmit diversityscheme from the previous transmission to the receiver station over thewireless network.

At step 390, the receiver combines the codewords of the retransmitpacket with the LDPC codewords from the original transmission using thestored LLR values to decode the codewords.

At step 395, the receiver resolves the retransmitted MPDUs using thedecoded LDPC codewords.

With regard to FIG. 4, a block diagram of operations and procedures 400for implementing an enhanced retransmission scheme is depicted accordingto embodiments of the present invention. The enhanced retransmissionscheme can be performed within a single transmission opportunity (TXPO)405 to reduce the amount of data stored in the buffers of thetransmitter and receiver and to reduce protocol complexity. The TXOP 405is a defined interval of time of the wireless network during which aparticular quality-of-service QoS station (STA) has the right toinitiate frame exchange sequences into the wireless medium.

In the example of FIG. 4, a data packet 410 is transmitted fromtransmitter STA1 to receiver STA2. STA2 sends an ACK (BA or CA) 420indicating which MPDUs or LDPC codewords were not received successfully.An enhanced re-transmission packet 415 is transmitted by STA1 and thereceiver can combine the original data packet 410 with the retransmitteddata packet 415 using LLRs stored from the original transmission. Theenhanced re-transmission packet 415 can be delivered using a differenttransmit diversity scheme. The STA2 then sends another ACK (BA or CA)425 indicating if the enhanced re-transmission packet 415 wassuccessfully received. If the TXOP 405 expires before the enhancedre-transmission packet 415 is successfully delivered, the receiver STA2abandons the stored LLR for data packet 410. STA1 can then start theprocess over and retransmit data packet 410 during the next TXOP.

With regard to FIG. 5, a block diagram of operations and procedures 500for implementing an enhanced retransmission scheme is depicted accordingto embodiments of the present invention. The enhanced retransmissionscheme can be performed within a single transmission opportunity (TXOP)505 to reduce the amount of data stored in the buffers of thetransmitter and receiver and to reduce protocol complexity. The TXOP 505is a defined interval of time during which a particularquality-of-service QoS station (STA) has the right to initiate frameexchange sequences into the wireless medium.

In the example of FIG. 5, a data packet 510 is transmitted fromtransmitter STA1 to receiver STA2. The data packet 510 has a PHY headeror MAC header that includes a HARQ Enable field 530 in this exampleindicating whether the enhanced re-transmission scheme is applied. Forexample, if the data packet 510 does not need any extra reliability, ora traditional ARQ is enough (because the BER is enough low), the HARQEnabled field 530 in the header is set to 0. This indicates that theenhanced re-transmission schemes will not be used for error recovery ofthe Data packet. Therefore, the transmitter will not request thecodewords from the receivers. Otherwise, the HARQ Enabled field 530 inthe header is set to 1. This indicates that the enhanced re-transmissionschemes will be used for error recovery of the data packet. In thiscase, the receiver prepares the codewords for error recovery, and thetransmitter can request the codewords from the receivers.

In the example of FIG. 5, the HARQ Enabled field 530 in the header isset to 1. Therefore, STA2 sends an ACK (BA or CA) 520 indicating whichMPDUs or LDPC codewords were not received successfully. An enhancedre-transmission packet 515 is transmitted by STA1 and the receiver cancombine the original data packet 510 with the retransmitted data packet515 using LLRs stored from the original transmission. The enhancedre-transmission packet 515 can be transmitted using a different transmitdiversity scheme. The STA2 then sends another ACK (BA or CA) 525indicating if the data was successfully received by the enhancedre-transmission method 515. If the TXOP 505 expires before the enhancedre-transmission packet 515 is successfully delivered, the receiver STA2abandons the stored LLR for data packet 510. STA1 can then start theprocess over and retransmit data packet 510 during the next TXOP.

The enhanced retransmission wireless packet transmitted in an enhancedretransmission scheme can be formatted in different ways according toembodiments of the present invention. In a first format depicted in FIG.6, the enhanced retransmission packet 600 does not include a MAC header.In this case, the packet is retransmitted with the missing codewords 610and 615 and a modified PHY preamble 605.

In a second format depicted in FIG. 7, the enhanced retransmissionwireless packet 700 includes a MAC header with a separate CRC encodedindependently from the re-transmitted codewords 715 and 720. To improvereliability, the codeword 710 for the MAC head and the CRC can betransmitted using a different modulation and coding scheme from there-transmitted codewords 715 and 720. The modulation scheme for thecodeword 710 of the MAC header and CRC and the modulation scheme for there-transmitted codewords 715 and 720 are signaled in a SIG field of PHYpreamble 705. The re-transmitted codewords are appended to the MACheader.

In a third format depicted in FIG. 8A, the enhanced retransmissionwireless packet 800 includes retransmitted codewords appended/prependedto another packet. For example, the retransmitted codeword can beappended to a PLCP Service Data Unit (PSDU) 810 that carries a new dataframe. The signaling for the PSDU is included in a SIG field of PHYpreamble 805 and a MAC header included in the PSDU 810. The signalingfor the retransmitted codewords 815 and 820 can be included in the SIGfield of the PHY preamble 805 or in the MAC header of the PSDU 810. ThePSDU 810 and the retransmitted codewords 815 and 820 can beindependently transmitted.

As depicted in FIG. 8B, the enhanced retransmission wireless packet 825can include retransmitted codewords appended/prepend to the PSDU 845that carries the AMPDU. Using the format depicted in FIG. 8B can reducethe amount of buffer required at the receiver. The signaling for theretransmitted codewords is contained in the SIG field of the PHYpreamble 830. The SIG field in the PHY preamble 830 indicates theretransmitted codewords 835 and 840.

According to some embodiments, a signal field of a PPDU 900 is used toindicate HARQ details for performing forward error-correcting coding andARQ error-control. For example, as depicted in FIG. 9A, a HARQ SIG field905 can contain signaling information for retransmission, such ascodeword index, station ID, and the modulating and coding scheme. TheHARQ SIG field is located before EHT-STF field 910 and EHT-LTF field915. The codewords 920 and 925 are transmitted based on the informationcontained in the HARQ SIG field 905.

According to some embodiments, HARQ SIG field 905 is located afterEHT-STF field 910 and EHT-LTF field 915.

As depicted in FIG. 9B, according to some embodiments of the presentinvention, in a multi-user (MU) PLCP Protocol Data Unit (PPDU) 975, eachUser Info field in the EHT-SIG-B 930 can carry the HARQ information forthe corresponding user. For example, as depicted in FIG. 9B, theEHT-SIG-B 930 includes information common to all users in Common Infofield 940, information associated with specific users, e.g., User1 Info935. The user information includes data rx parameters 945 and codewordrx parameters 950.

Exemplary Computer Controlled System

Embodiments of the present invention are drawn to electronic systems forenhanced data retransmission based on LLR combining in WLAN. Accordingto some embodiments, wireless data packets can be retransmitted using amodified transmission scheme. Packets that are received with an errorare stored, and a subsequent packet is received that includes data thatcan be used to correct the error. The following discussion describes onesuch exemplary electronic system or computer system can be used as aplatform for implementing embodiments of the present invention as areceiver station and/or a transmitter station.

In the example of FIG. 10, the exemplary computer system 1012 (e.g., awireless access point or a wireless station) includes a centralprocessing unit (CPU) 1001 for running software applications andoptionally an operating system. Random access memory 1002 and read-onlymemory 1003 store applications and data for use by the CPU 1001. Datastorage device 1004 provides non-volatile storage for applications anddata and may include fixed disk drives, removable disk drives, flashmemory devices, and CD-ROM, DVD-ROM or other optical storage devices.The optional user inputs 1006 and 1007 comprise devices that communicateinputs from one or more users to the computer system 1012 (e.g., mice,joysticks, cameras, touch screens, and/or microphones).

A communication or network interface 1008 includes a plurality oftransceivers and allows the computer system 1012 to communicate withother computer systems, networks, or devices via an electroniccommunications network, including wired and/or wireless communicationand including an Intranet or the Internet (e.g., 802.11 wirelessstandard). The communication or network interface 1008 and can include atransmitter and a separate receiver for sending and receiving wirelessdata.

The optional display device 1010 may be any device capable of displayingvisual information in response to a signal from the computer system 1012and may include a flat panel touch sensitive display, for example. Thecomponents of the computer system 1012, including the CPU 1001, memory1002/1003, data storage 1004, user input devices 1006, and graphicssubsystem 1005 may be coupled via one or more data buses 1000.

Some embodiments may be described in the general context ofcomputer-executable instructions, such as program modules, executed byone or more computers or other devices. Generally, program modulesinclude routines, programs, objects, components, data structures, etc.that perform particular tasks or implement particular abstract datatypes. Typically the functionality of the program modules may becombined or distributed as desired in various embodiments.

Embodiments of the present invention are thus described. While thepresent invention has been described in particular embodiments, itshould be appreciated that the present invention should not be construedas limited by such embodiments, but rather construed according to thefollowing claims.

What is claimed is:
 1. A method of data retransmission in a wirelessnetwork, the method comprising: transmitting a wireless packetcomprising an aggregated MAC Protocol Data Unit (AMPDU) comprising aplurality of MAC Protocol Data Units (MPDUs) and codewords associatedwith the MPDUs; receiving an acknowledgement from a receiver indicatingfailed MPDUs of the AMPDU that were received with error, wherein thereceiver stores log-likelihood ratios (LLRs) for a set of codewordsassociated with the failed MPDUs; and responsive to the acknowledgement,transmitting a set of codewords to the receiver for performing chasecombining to resolve the MPDUs of the AMPDU in a retransmission packetcomprising a SIG field signaling a modulation scheme for transmittingthe codewords, wherein the receiver chase combines the set of codewordswith the codewords associated with the MPDUs using the stored LLRs togenerate combined codewords, decodes the combined codewords to generatedecoded codewords, and resolves the MPDUs of the AMPDU using the decodedcodewords.
 2. The method as described in claim 1, wherein the codewordsassociated with the MPDUs and the set of codewords comprise LDCPcodewords, and the wireless network is a WiFi network.
 3. The method asdescribed in claim 1, wherein the transmitting a wireless packetcomprising an AMPDU comprises using a first spatial stream, and thetransmitting the set of codewords comprises using a second spatialstream.
 4. The method as described in claim 1, wherein the transmittinga wireless packet comprising an AMPDU comprises using a firstbeamforming technique, and the transmitting the set of codewordscomprises using a second beamforming technique.
 5. The method asdescribed in claim 1, wherein retransmitting the set of codewordscomprises retransmitting a minimum set of codewords that contain thefailed MPDUs.
 6. The method as described in claim 5, wherein theacknowledgement is a block acknowledgment (BA), and further comprisingidentifying the minimum set of codewords required to be retransmittedbased on an index of the BA.
 7. The method as described in claim 1,wherein the MPDUs are segmented and each codeword is associated with arespective single MPDU.
 8. A method of data retransmission in a wirelessnetwork, the method comprising: receiving a wireless aggregated MACProtocol Data Unit (AMPDU) comprising a plurality of MAC Protocol DataUnits (MPDUs) and codewords associated with the MPDUs from a transmitterof the wireless network; transmitting a wireless acknowledgement to thetransmitter indicating failed MPDUs of the AMPDU that were received witherror; storing log-likelihood ratios (LLRs) in memory for a set ofcodewords associated with the failed MPDUs; receiving a wirelesslyretransmitted set of codewords over the wireless network for performingchase combining to resolve the MPDUs of the AMPDU in a retransmissionpacket comprising a SIG field signaling a modulation scheme used totransmit the codewords; chase combining the retransmitted set ofcodewords with the codewords associated with the MPDUs using the storedLLRs to generate combined codewords; decoding the combined codewords togenerate decoded data; and resolving the MPDUs of the AMPDU using thedecoded data.
 9. The method as described in claim 8, wherein thecodewords and the retransmitted set of codewords comprise LDCPcodewords, and the wireless network is a WiFi wireless network.
 10. Themethod as described in claim 8, wherein the AMPDU is transmitted by thetransmitter using a first spatial stream, and the retransmitted set ofcodewords is transmitted by the transmitter using a second spatialstream.
 11. The method as described in claim 8, wherein the AMPDU istransmitted by the transmitter using a first beamforming technique, andthe retransmitted set of codewords is transmitted by the transmitterusing a second beamforming technique.
 12. The method as described inclaim 8, wherein the retransmitted set of codewords comprises a minimumset of codewords that contain the failed MPDUs.
 13. The method asdescribed in claim 12, wherein the acknowledgement is a blockacknowledgment (BA) comprising a respective bit for each MPDU of saidAMPDU, and the minimum set of codewords required to be retransmitted isdetermined by the transmitter based on an index of the BA.
 14. A systemfor data retransmission in a wireless network, the system comprising: awireless transmitter; and a wireless receiver, wherein: the transmitteris operable to transmit an aggregated MAC Protocol Data Unit (AMPDU)comprising a plurality of MAC Protocol Data Units (MPDUs) and codewordsassociated with the MPDUs to the receiver; the receiver is operable totransmit a codeword acknowledgement (CA) to the transmitter, wherein theCA indicates failed codewords of the AMPDU that were received with errorto the transmitter; the receiver is operable to store log-likelihoodratios (LLRs) in memory for the failed codewords; the transmitter isoperable to retransmit codewords to the receiver for performing chasecombining to resolve the MPDUs of the AMPDU in a retransmission packetcomprising a SIG field signaling a modulation scheme for retransmittedcodewords; the receiver is operable to chase combine the retransmittedcodewords with the failed codewords of the AMPDU using the stored LLRsto generate combined codewords; the receiver is operable to decode thecombined codewords to generate decoded data; and the receiver isoperable to resolve the MPDUs of the AMPDU using the decoded data. 15.The system as described in claim 14, wherein the failed codewords andthe retransmitted codewords comprise LDCP codewords, and the wirelessnetwork is a WiFi wireless network.
 16. The system as described in claim14, wherein the AMPDU is transmitted by the transmitter using a firstspatial stream, and the failed codewords are retransmitted by thetransmitter using a second spatial stream.
 17. The system as describedin claim 16, wherein the AMPDU is transmitted by the transmitter using afirst set of frequency segments, and the failed codewords aretransmitted by the transmitter using a second set of frequency segments.18. The system as described in claim 14, wherein the AMPDU istransmitted by the transmitter using a first transmit quadratureamplitude modulation (QAM) mapping, and the failed codewords areretransmitted by the transmitter using a second QAM mapping.
 19. Thesystem as described in claim 14, wherein the AMPDU is transmitted by thetransmitter using a first tone interleaver, and the failed codewords aretransmitted by the transmitter using a second tone interleaver.
 20. Thesystem as described in claim 14, wherein the retransmission packetcomprises an enacted retransmission packet comprising a PHY header, andthe PHY header comprises the SIG field.